Rio Grande silvery minnows spawn in Big Bend

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By Sue M. Holmes

ALBUQUERQUE — The U.S. Fish and Wildlife Service says Rio Grande silvery minnows stocked in the Big Bend area of the river in Texas have successfully spawned — a step in establishing the endangered fish outside the middle Rio Grande in New Mexico.

Biologists identified the river’s Big Bend reach as the most likely spot to support the fish in the species’ historic range.

Officials released 445,000 silvery minnows from New Mexico breeding facilities in 2008 in Big Bend Ranch State Park, Big Bend National Park and a privately owned conservation area. They released 509,000 more last year.

This spring, they collected eggs from that part of the river to see what species were spawning, and identified some silvery minnow eggs.

That doesn’t mean the restoration project is successful, “but it’s a first step, the first milestone we have to reach to document that it will succeed,” said Jason Remshardt, Fish and Wildlife’s supervisory biologist for the minnow.

Project officials expected the species would spawn at some point, but “that it happened this year was a little unexpected,” he said.

The spawning shows the project could potentially be successful in re-establishing the silvery minnow, said Fish and Wildlife biologist Aimee Roberson, who is based in Texas near Big Bend.

The Rio Grande in south Texas is a very different river from what it is in New Mexico, and biologists weren’t sure conditions would be right for minnows to spawn in the Big Bend.

Roberson remembers when Remshardt called her to say genetic tests confirmed silvery minnow eggs.

“I literally was jumping up and down and cheering. I was so excited,” she recalled. “We’ve been working on this for years, and to have this significant event shows we’re moving in the right direction.”

The Rio Grande silvery minnow, which grows to about 3.5 inches, was once one of the most widespread native fish in the Rio Grande and Pecos River, found from northern New Mexico to the Gulf of Mexico at Texas.

Before fish were released in the Big Bend, the species had dwindled to a 170-mile stretch of the middle Rio Grande in New Mexico — about 5 percent of its historic range.

The decline has been attributed to construction of dams and reservoirs, modification of river flows, habitat fragmentation and decreasing water quality.

The recovery project plans to stock fish in the Big Bend reach for five years. Some 200,000 silvery minnows are to be released in October.

Biologists won’t start figuring out how many fish exist in the area until summer 2011, Remshardt said. Silvery minnows are being stocked in four Big Bend sites, and biologists will not only check for fish in those areas, but also see whether they’ve “sort of filled in the holes in our stocking areas,” he said.

The Texas minnows are considered a nonessential, experimental population — meaning not all requirements of the Endangered Species Act apply. Remshardt said that makes reintroduction “more palatable” for other water users.

“It gave us the best opportunity to get the work accomplished but still give the fish the protection it needs,” he said.

The Fish and Wildlife Service wants self-sustaining populations in at least three areas of the minnow’s historic range outside New Mexico’s middle Rio Grande.